The present invention relates generally to an endless track tensioning system. More particularly, the invention is directed to a track tensioning system that automatically relieves tension in an endless track when the endless track encounters an obstruction and does so in a manner that limits how much slack may be introduced into the endless track but allows for the introduction of additional slack to remove the endless track for servicing and/or replacement.
A crawler-type work vehicle is typically supported and propelled by an undercarriage assembly having an endless track entrained about a drive roller or sprocket, a front idler roller, a rear idler roller, and a series of track rollers. The drive roller or sprocket is driven by an engine of the work vehicle which in turn causes the endless track to be advanced around each of the front and rear idler rollers as well as the track rollers to move the work vehicle in either a forward or reverse direction.
For the endless track to function properly, it must be tensioned taut around the several rollers. If the endless track is not properly tensioned, the track may derail from the drive sprocket or roller and the idler rollers. To this end, a tensioning mechanism is used in order to create the tension necessary to keep the track from derailing from the drive sprocket or roller and the idler rollers. In one form, the tensioning mechanism may be a coiled spring that urges the front idler roller in a direction away from the rear roller, thereby creating tension on the track. Over a period of time, a number of the components associated with the undercarriage assembly, such as the track and the idler rollers, begin to wear thereby creating slack in the track. In order to remove the slack from the track chain, it is necessary to increase the tension of the track chain to prevent undesired derailing of the track.
While it is generally desired to maintain tension in the track, there are times during operation of the work vehicle in which it is desired to introduce, albeit temporarily, slack into the endless track. For example, if the track of the work vehicle encounters a hard object such as a rock or stone with significant force, it is necessary to momentarily relieve the tension to ensure that the track is not damaged. Thus, a number of tensioning mechanisms are designed to momentarily relieve the tension in the track during such conditions. This is commonly accomplished by using a coiled spring that may compress somewhat to allow the idler roller to move away from the track and, as a result, relieve tension in the track until the obstacle is cleared. Once the obstacle is cleared, the track is automatically re-tensioned by the spring.
Typically, the spring is used in combination with a grease-type cylinder that moves the idler roller outwardly to tension the track and inwardly to introduce slack in the track in order to allow the track to be removed for servicing or replacement. The grease-type cylinder is isolated from the hydraulic system of the vehicle and is manually operated, in that an operator must stand at the vehicle and introduce grease to the appropriate side of the cylinder to extend or retract the cylinder, and must open a fitting on the opposite side of the cylinder to allow the grease to be expelled. This process is messy, wasteful and time consuming, and makes the task of changing tracks very difficult and challenging.
Therefore, there is a need for a track tensioning mechanism that eliminates the use of a grease cylinder and can be used in connection with the hydraulic system of the vehicle while isolating the hydraulic system from shocks experienced with the track encounters an obstacle, and which can temporarily relieve tension in the endless track when necessary without introducing undesirable excessive slack in the endless track during such conditions that could cause the track to derail.